Optical sub-assembly having an enhanced discharge-resistant arrangement and an optical transceiver using the same

ABSTRACT

An optical assembly of the present invention comprises a package installing a semiconductor optical device therein, a metal sleeve attached to the package, and the resin holder disposed between package and the sleeve member. When this optical assembly is installed within the optical transceiver and even the metal sleeve extrudes into the optical receptacle and is exposed to the outside there, the EMI noise can be prevented from importing into the transceiver and radiating to the outside, because the resin holder made of substantially insulating material is disposed between the sleeve and the package.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical subassembly that installs alight-emitting device or a light-receiving device therein, inparticular, relates to a structure for enhancing the tolerance againstthe electro-static discharge.

2. Related Prior Art

The conventional structure of an optical subassembly (hereinafterdenoted as OSA) comprises a CAN-type package for installing alight-emitting or light-receiving device and an alignment memberincluding a plurality of cylindrical members connected to the headportion of the CAN package. The CAN package, including a stem and a capboth made of metal, installs the light-emitting device such as laserdiode (LD) onto the stem so as to coincide the optical axis of the laserdiode with the center axis of the cylindrical members. On the headportion of the cap may be provided with a lens for concentrating thelight emitted from the LD.

For such CAN-type package with the LD, the cylindrical member aligns andoptically couples the LD with the distal end of an optical fiber. Thatis, the plurality of cylindrical members may align the optical axis ofthe LD in the XY plane, which intersecting the optical axis, and alongthe Z-direction parallel to the optical axis. After alignment, thecylindrical members are welded not only to each other but also to theCAN package to secure the optical alignment permanently. An opticaltransceiver is completed to install such OSAs therein and to connect theOSA to the electronic circuit provided on a circuit board.

In the conventional OSA, fixing of cylindrical members to each other orto the CAN package used to be carried out with the YAG laser welding. Inthe YAG laser welding, optical beams output from the YAG laser withextreme power are irradiated in short time to points to be welded tocause melt locally. In order to melt locally with the optical beam, themembers to be welded are limited to materials with low thermalconductivity in addition to the mechanical stiffness. Therefore, metalswith low thermal conductivity, such as iron (Fe), stainless steel, andKovar™, are used to the cylindrical member.

On the other hand, the OSA is installed within the transceiver as thecylindrical member thereof projects into the optical receptacle of thetransceiver. Here, the optical receptacle is formed in the front side ofthe optical transceiver and receives an optical connector to couple theoptical fiber secured in the optical connector with the LD in the CANpackage. In this arrangement, since the cylindrical member made of metalis exposed outside of the transceiver, the cylindrical member mayoperate as an antenna to import the noise from the outside or to exportthe noise to the outside as an electromagnetic interference (EMI).Moreover, the optical connector with the static charge mates with theOSA in the receptacle, this static charge is conveyed to the circuitboard installed in the transceiver via the metal OSA, consequentlybreaks the circuit element mounted thereon.

To make the OSA with resin, in particular, a portion of the cylindricalmember thereof, will solve at least above subject. However, the resinsleeve tends to be affected by the abrasion due to the sleeve insertinginto or extracting from the sleeve. Moreover, since the resin sleeve isinferior in holding the ferrule therein to the metal sleeve, the resinsleeve is unsuitable to the single mode fiber having a relatively smallcore.

SUMMARY OF THE INVENTION

Therefore, an object of the present invention is to solve subjects abovedescribed. A feature of the invention is that a part of the cylindricalmember is made of insulating material or made of material having areasonable conductivity, namely, the electrical conductivity able toconvey the static discharge within a range not breaking the circuitelement.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross section showing an OSA according to the firstembodiment of the invention;

FIG. 2 is a cross section showing another OSA according to the secondembodiment of the invention;

FIG. 3 is a cross section showing still another OSA according to thethird embodiment of the invention;

FIG. 4 is an exploded view showing an optical transceiver installing theOSA of the invention; and

FIG. 5 is a schematic diagram that shows how the static discharge isconveyed to the inside of the optical transceiver through the OSA.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Next, preferred embodiments of the present invention will be described.In drawings and their explanations, same elements will be referred bysame numerals or symbols without overlapping explanations.

First Embodiment

FIG. 1 is a side view, partially cutaway, showing an optical subassembly1 (hereinafter denoted as OSA) according to the first embodiment of theinvention, FIG. 1A is a perspective view and FIG. 1C is an exploded viewof the OSA.

The OSA comprises a CAN type package 11, a sleeve 13, a resin holder 12and a metal holder 14. These two holders, 12 and 14, are sandwichedbetween the CAN package 11 and the sleeve 13.

The CAN package 11, providing a stem 11 a and a cap 11 b, installs asemiconductor optical device 15 on the stem 11 a. The semiconductoroptical device 15 may be a semiconductor laser diode (LD) or asemiconductor light-emitting diode (LED) for the case that the OSA is atransmitting optical subassembly (TOSA), while the device 15 may be aphotodiode (PD) for the case that the OSA is a receiving opticalsubassembly (ROSA). Although not shown in figures, a plurality of leadpins is extracted from the stem 11 a to supply electrical signals and tosupply electric power to the semiconductor optical device. The stem 11 aand the cap 11 b are made of metal such as iron (Fe), and Kovar^(M). Theconnection between the stem 11 a and the cap 11 b may be carried out bythe resistance welding at the brim portion of the stem 11 a. In FIG. 1,a lens for concentrating light is mounted on a center portion of thesealing in the cap 11 b, but is not always provided in the cap.

The resin holder 12 is a member made of resin and positioned in thefront portion of the CAN package. Typical material for the resin holderis poly-phenylene sulfide (PPS). The connection between the resin holderand the CAN package is carried out with adhesive. Both of theultraviolet curing adhesive and the heat curable adhesive may be usedfor the connection. This resin holder may be formed by the insertionmold, in which the resin is molded within the die with the metal.

The metal holder 14 is sandwiched between the resin holder 12 and themetal sleeve 13. The metal holder is made of, for instance, stainlesssteel and has a disk shape. A hollow 14 a is formed in the centerportion at the surface facing the resin holder 12 to receive theprotruding portion 12 a in the center of the resin holder 12. Theprotruding portion 12 a of the resin holder 12 is press-fitted into thehollow 14 a in the metal holder 14. The bond strength between these twoholders 12, 14 may be enhanced, in addition to this press fitting, byproviding the adhesive therebetween. FIG. 1A illustrates that thediameter of the resin holder 12 and that of the metal holder 14 aredifferent to each other. However, these two diameters may be made equalto each other.

The sleeve 13, provided in the front side of the CAN package and made ofmetal, has a cylindrical shape. By receiving the ferrule, which is notshown in FIG. 1A and secured in the distal end of the optical fiber, inthe bore of the cylinder, the sleeve makes the optical fiber positionedin the center of the ferrule couple with the semiconductor opticaldevice installed within the CAN package. The sleeve is typically made ofstainless steel in the case of the metal sleeve. When the optical fiberinserted thereinto is a single mode fiber, the optical coupling betweensuch optical fiber and the semiconductor optical device 16 requires theaccuracy of a micron meter or less. While, after the optical couplingbetween the optical fiber and the optical device 16 is once established,and the sleeve 13 and the metal holder 14 are so positioned, the opticalcoupling condition should not be affected by the ferrule inserting intoor extracting from the sleeve. Thus, the sleeve 13 requires thestiffness in addition to the dimensional accuracy, so the stainlesssteel is optimum material for the sleeve 13.

The other surface 14 b of the metal holder 14, namely the surface facingthe sleeve 13, is processed in flat to enable the optical alignmentbetween the optical fiber secured in the ferrule and the semiconductoroptical device 16 by sliding the sleeve 13 on this surface 14 b. On thecenter portion of the metal holder 14 is provided with an opening 14 dto pass light. The diameter of this opening is smaller than the innerdiameter of the sleeve 13 to make the ferrule inserted into the sleeve13 butt to this other surface 14 b of the metal holder, thus positioningthe ferrule along the optical axis, hereinafter denoted as Z-direction,in the sleeve 13. The alignment within the plane, namely the XY-planethat is perpendicular to the optical axis, is carried out by sliding thesleeve 13 on the other surface 14 b of the metal holder 14.Specifically, for the case of the TOSA, under the condition that theferrule with the optical fiber is inserted into the sleeve, thelight-emitting device 16 such as semiconductor laser diode mounted onthe stem 11 a is practically operated, and the magnitude of the opticaloutput power from the optical fiber is monitored, the sleeve is fixed atthe position where the monitored magnitude of the output light becomes apredefined value. In the case of the ROSA, under the condition that thesignal light is guided into the optical fiber, which is inserted intothe sleeve with the ferrule, and the optical power is monitored by thesemiconductor optical device mounted in the optical device, the sleeveis aligned at the position where the magnitude monitored by the opticaldevice becomes a maximum. The connection between the sleeve 13 and themetal holder 14 may be done by the YAG laser welding. That is, the endof the sleeve 13 provides a flange and this flange is welded with YAGlaser to the metal holder 14. Occasionally, the sleeve 13 without anyflange in the end portion thereof may be welded to the metal holder 14.Since the YAG laser may weld both materials in quite short time byoptical pulses with high power, the optical misalignment occurred duringthe solidification of materials may be prevented. On the outer surfaceof the sleeve is provided with some flanges 13 c to position theassembly 1 in the optical transceiver.

Thus, according to the present configuration of the optical assembly 1,since the resin holder 12, made of substantially insulating material, isinserted between the CAN package 11 and the metal sleeve 13, it isprevented to convey the static electricity from the charged opticalconnector to the CAN package or to the electronic circuit board, evenwhen this optical assembly 1 is installed in the optical transceiver andthe static electricity is conveyed to the metal sleeve positioned in theoptical receptacle. Another material may be applicable for the resinholder, in which such material has a moderate conductivity only toconvey the static electricity not breaking the circuit element.

Second Embodiment

FIG. 2A shows the second embodiment of the present invention, FIG. 2B isa perspective view and FIG. 2C is an exploded view of the secondembodiment. In the present embodiment, the resin holder 12 and the metalholder are provided between the CAN package 11 and the sleeve 13. Theshape of the resin holder 12 is different to that shown in the firstembodiment.

The resin holder 12 comprises a first portion 12 a having a disk shapeand a second portion 12 b. The shape of the first portion 12 a issimilar to that shown in the former embodiment.

The resin holder 12 is fixed to the metal holder 14 by the pressfitting, by the press fitting with the adhesive, or by the insertionmolding with the metal holder 14. The press fitting is performed suchthat, the diameter of the protruding portion 12 a is set to be slightlygreater than the diameter of the hollow 14 a provided in the center ofthe metal holder 14, the protruding portion 12 a is press-fitted intothe hollow 14 a. The second portion 12 b of the resin holder 12,extending from the first portion 12 a, covers the side surface of theCAN package 11. The connection between the CAN package 11 and the secondportion 12 a of the resin holder 12 is done by the adhesive.

In the present embodiment, the optical alignment along the Z-directioncan be carrier out by sliding the CAN package within the second portion12 b of the resin holder. The alignment along X and Y directions may bedone, as mentioned in the first embodiment, by sliding the sleeve 13 onthe surface of the metal holder 12. The connection between the metalholder 14 and the sleeve 13, as shown in the previous embodiment, isdone by the YAG laser welding, while the connection between the resinholder and the CAN package may be done by the ultraviolet curingadhesive or by the heat curable adhesive. For the ultraviolet adhesive,to metallize the inner surface of the second portion 12 b is effective,because the light for curing may reach the depth of the resin holder 12by the multiple reflection between this inner surface of the resinholder 12 and the outer surface of the CAN package 11.

Third Embodiment

FIG. 3 is a side view showing the third embodiment of the invention. Inthis embodiment, in addition to the second embodiment, the metal holder14 has a characteristic shape.

The metal holder 14 comprises a disk-shaped first portion 14 a and acylindrical second portion 14 b. The second portion fully covers thesecond portion of the resin holder 12. The resin holder 12 is fixed tothe metal holder by the press fitting or by the press fitting togetherwith the adhesive, or is formed by the insertion mold with the metalholder 14. The press fitting is performed such that, the diameter of theprojection 12 c is slightly greater than that of the hollow provided inthe center of the first portion 14 a is of the metal holder 14, theprojection 12 c is pressed into the hollow.

The connection between the metal holder 14 and the sleeve 13, similar tothe first and second embodiments, is done by the YAG laser welding,while the connection between the resin holder 12 and the CAN package 11is done by the adhesive. In these second and third embodiments, the bondstrength between the resin holder 12 and the CAN package 11 can beenhanced because the area to be connected may be widened in theseembodiments. Moreover, the optical alignment along the Z-direction maybe carried out, therefore, the optical coupling with high couplingefficiency may be obtained.

Fourth Embodiment

FIG. 4 is an exploded view showing an optical transceiver installing theOSA, the TOSA and ROSA, according to the present invention.

The optical transceiver comprises a base, a cover, the ROSA and theTOSA, and an OSA holder. Within a space defined by the base and thecover and formed behind the TOSA and the ROSA is provided with a circuitboard installing an electronic circuit. This electronic circuit includesa driver for processing the signal input from the outside of thetransceiver and driving the light-emitting device within the TOSAby thusprocessed signal and a signal processor for amplifying a signalconverted by the light-receiving device within the ROSA and outputtingthus amplified signal to the outside of the transceiver.

The TOSA/ROSA is positioned against the base by sandwiching the flangeprovided in the stem of the TOSA/ROSA between the OSA holder and thestructure provided in the base. At the position thus fixed, the distalend, the side of the sleeve, of the TOSA/ROSA extrudes within theoptical receptacle, and the semiconductor optical device installedwithin the TOSA/ROSA can optically couple with the optical fiber securedin the optical plug inserted into the optical receptacle.

In the transceiver, the distal end of the TOSA/ROSA is covered with anOSA cover. Although the sleeve is necessary to couple with the opticalfiber, when the sleeve is exposed within the optical receptacle, theposition thereof easily varies from the optimum position for the opticalcoupling. Therefore, the OSA cover may prevent this positional deviationof the sleeve.

The base, the OSA holder and the OSA cover may be generally made ofresin. On the other hand, the TOSA/ROSA is made primarily of metal, asmentioned in the previous embodiment, from various viewpoints such asthe optical coupling accuracy, the robustness of the optical couplingand the cost merit, therefore, only the sleeve is exposed to the outsideof the transceiver. Accordingly, this metal sleeve operates as anantenna for the electromagnetic noise to radiate to the outside or togather from the outside. For such condition, by inserting the resinmember between the metal sleeve and the metal package, this antennaeffect can be prevented.

Thus, the invention has been described. Although the explanation aboveis referred mainly to the TOSA, the configuration of the OSA accordingto the present invention can be easily applied to the ROSA.

1. An optical assembly, comprising: a semiconductor optical device; apackage for installing said semiconductor optical device; a metal sleevemember coupled to said package; and a resin holder disposed between saidpackage and said metal sleeve member, wherein said resin holder issubstantially insulating.
 2. The optical assembly according to claim 1,further comprises a metal holder disposed between said metal sleevemember and said resin holder.
 3. The optical assembly according to claim2, wherein said package is a co-axial type package including adisk-shaped stem for mounting said semiconductor optical device and acap extending from said disk-shaped stem, and said resin holder includesa disk-shaped first portion and a cylindrical-shaped second portionextending from said first portion, said second portion covering a sideof said cap of said package.
 4. The optical assembly according to claim3, wherein said metal holder includes a disk-shaped portion and acylindrical portion extending from said disk-shaped portion of saidmetal holder, said cylindrical portion covering said second portion ofsaid resin holder without being in contact with said stem of saidpackage.
 5. The optical assembly according to claim 2, wherein said capprovides a lens on an optical axis of said semiconductor optical device,and said resin holder provides a hollow for receiving said lens in asurface facing said cap.
 6. The optical assembly according to claim 2,wherein said resin holder provides a protrusion in a surface facing saidmetal holder, and said metal holder provides a hollow to receive saidprotrusion in a surface facing said resin holder.
 7. The opticalassembly according to claim 6, wherein said protrusion in said resinholder is press-fitted into said hollow of said metal holder.
 8. Theoptical assembly according to claim 2, wherein said metal holderprovides a diameter greater than a diameter of said resin holder.
 9. Theoptical assembly according to claim 1, wherein said package provides alens on an optical axis of said semiconductor optical device, and saidresin holder provides a hollow to receive said lens in a surface facingsaid package.
 10. An optical transceiver for an optical signal totransmit to and receive from an optical fiber by mating with an opticalconnector having said optical fiber, said optical transceivercomprising: an optical assembly according to claim 1; a substrate forelectrically coupling to said optical assembly; an assembly holder forfixing said optical assembly; a body including first to third portions,said first portion providing an optical receptacle for receiving saidoptical connector, said second portion fixing said optical assemblyco-operated with said assembly holder, and said third portion installingsaid substrate; and a cover for covering said optical assembly, saidsubstrate and said assembly holder, wherein said metal sleeve member ofsaid optical assembly protrudes into said optical receptacle to matewith said optical connector for coupling said semiconductor opticaldevice installed in said optical assembly with said optical fibersecured in said optical connector.
 11. The optical assembly according toclaim 10, further comprises a metal holder disposed between said metalsleeve member and said resin holder.
 12. The optical assembly accordingto claim 11, wherein said package is a co-axial type package including adisk-shaped stem for mounting said semiconductor optical device and acap extending from said disk-shaped stem, and said resin holder includesa disk-shaped first portion and a cylindrical-shaped second portionextending from said first portion, said second portion covering a sideof said cap of said package.
 13. The optical assembly according to claim12, wherein said metal holder includes a disk-shaped portion and acylindrical portion extending from said disk-shaped portion of saidmetal holder, said cylindrical portion covering said second portion ofsaid resin holder without being in contact with said stem of saidpackage.
 14. The optical assembly according to claim 11, wherein saidcap provides a lens on an optical axis of said semiconductor opticaldevice, and said resin holder provides a hollow for receiving said lensin a surface facing said cap.
 15. The optical assembly according toclaim 11, wherein said resin holder provides a protrusion in a surfacefacing said metal holder, and said metal holder provides a hollow toreceive said protrusion in a surface facing said resin holder.
 16. Theoptical assembly according to claim 15, wherein said protrusion in saidresin holder is press-fitted into said hollow of said metal holder. 17.The optical assembly according to claim 11, wherein said metal holderprovides a diameter greater than a diameter of said resin holder. 18.The optical assembly according to claim 10, wherein said packageprovides a lens on an optical axis of said semiconductor optical device,and said resin holder provides a hollow to receive said lens in asurface facing said package.